Apoptosis-Inducing Agent for Prostate Cancer Cells

ABSTRACT

According to the present invention, an apoptosis-inducing agent for prostate cancer comprising REIC/Dkk-3 DNA or an REIC/Dkk-3 protein, and a therapeutic agent for prostate cancer and an agent for inhibiting prostate cancer metastasis that comprise such apoptosis-inducing agent are provided. 
     An apoptosis-inducing agent for prostate cancer, comprising, as an active ingredient, an REIC/Dkk-3 protein (a) or (b) or REIC/Dkk-3 DNA (c) or (d):
         (a) a protein consisting of the amino acid sequence represented by SEQ ID NO: 2;   (b) a protein consisting of an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO: 2 by substitution or deletion of 1 or more amino acids;   (c) DNA consisting of the nucleotide sequence represented by SEQ ID NO: 1; or   (d) DNA that hybridizes under stringent conditions to DNA consisting of a nucleotide sequence complementary to the nucleotide sequence represented by SEQ ID NO: 1 and encodes a protein having apoptosis activity; and   a therapeutic agent for prostate cancer comprising such apoptosis-inducing agent are provided

TECHNICAL FIELD

The present invention relates to apoptosis induction in prostate cancer cells with the use of the REIC/Dkk-3 gene, which is a tumor-inhibiting gene, an apoptosis-inducing agent for prostate cancer cells, which comprises the REIC/Dkk-3 gene or an expression product thereof, and a therapeutic agent for prostate cancer and an agent for inhibiting prostate cancer metastasis, which comprise the apoptosis-inducing agent.

BACKGROUND ART

Selective elimination of cancer cells is an important key issue in treating cancer. During malignant conversion and progression, various genetic changes occur in cells (Vogelstein, B. et al., Trends Genet 9, 138-41 (1993)). Such mutations could be targets of gene therapies for cancer.

Some types of genes exhibit a selective killing effect on cancer cells when overexpressed. Representative examples of such genes include p 53 (Chen, P. L. et al., Science 250, 1576-80 (1990); Fujiwara, T. et al., J Natl Cancer Inst 86, 1458-62 (1994); and Nielsen, L. L. et al., Cancer Gene Ther 4, 129-38 (1997)) and mda-7 (Fisher, P. B. et al., Cancer Biol Ther 2, S23-37 (2003)), which have been known as antioncogenes.

Meanwhile, the REIC/Dkk-3 gene has been known as a gene involved in cell immortalization. It has been reported that expression of the gene is inhibited in cancer cells (see WO01/038523, Tsuji, T. et al., BiochemBiophys Res Commun 268, 20-4 (2000), Tsuji, T. et al., BiochemBiophys Res Commun 289, 257-63 (2001), Nozaki, I. et al., Int J Oncol 19, 117-21 (2001) and Kurose, K. et al., J Urol 171, 1314-8 (2004)).

The REIC/Dkk-3 gene is a member of the Dkk family and has been known to interfere with Wnt signal transduction via Wnt receptors (see Bafico, A. et al., Nat Cell Biol 3, 683-6 (2001) and Hoang, B. H. et al., Cancer Res 64, 2734-9 (2004)). The Wnt genes play pleiotropic roles in critical biological contexts, including cell growth, differentiation, malignant transformation, and the like (see Moon, R. T. et al., Science 296, 1644-6 (2002)). Therefore, similarly, Dkk family members (including 4 genes that have been known to exist in humans) are thought to fulfill important functions regarding cell growth, differentiation, and malignant transformation. However, most of their functions have not yet been elucidated.

DISCLOSURE OF THE INVENTION

It is an objective of the present invention to provide an apoptosis-inducing agent for prostate cancer cells, which comprises REIC/Dkk-3 DNA or the REIC/Dkk-3 protein, and a therapeutic agent for prostate cancer and an agent for inhibiting prostate cancer metastasis, which comprise the apoptosis-inducing agent.

The present inventors have conducted intensive studies of the previously reported relationship between the REIC/Dkk-3 gene and cancer cells. It was discovered that the expression level of the REIC/Dkk-3 gene is reduced in human cancer cell lines and cancer tissue. The downregulation of the REIC/Dkk-3 gene was partially caused by promoter hypermethylation. Overexpression of the REIC/Dkk-3 gene with the use of vectors caused growth inhibition in human osteosarcoma cells. These findings indicate that the REIC/Dkk-3 gene could function as an antioncogene and thus that the REIC/Dkk-3 gene could be a new therapeutic target for human cancer.

In addition, the present inventors have found that the expression level of the REIC/Dkk-3 gene is reduced in highly malignant prostate cancer cells. Thus, they have conducted further intensive studies of the use of the REIC/Dkk-3 gene as a therapeutic agent for prostate cancer. Also, the present inventors have found that it is possible to inhibit prostate cancer by causing REIC/Dkk-3 gene expression in prostate cancer cells so as to induce apoptosis in prostate cancer cells. This has led to the completion of the present invention.

Further, the present inventors have examined effects of prostate cancer metastasis inhibition by the REIC/Dkk-3 gene. As a result, they have found that the REIC gene has metastasis-inhibitory activity in mouse orthotopic transplantation models of prostate cancer, in addition to its localized tumor-inhibitory activity.

Furthermore, the present inventors have found that the combined use of the REIC/Dkk-3 gene and hyperthermia results in the improvement in the effects of prostate cancer treatment and prostate cancer metastasis inhibition.

As a result, the present inventors have completed the present invention.

Specifically, the present invention is described as follows.

-   [1] An apoptosis-inducing agent for prostate cancer, comprising, as     an active ingredient, the following REIC/Dkk-3 protein:

(a) a protein consisting of the amino acid sequence represented by SEQ ID NO: 2; or

(b) a protein consisting of an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO: 2 by substitution, deletion, or addition of 1 or more amino acids and having apoptosis activity.

-   [2] A therapeutic agent for prostate cancer, comprising the     apoptosis-inducing agent according to [1]. -   [3] An apoptosis-inducing agent for prostate cancer, comprising, as     an active ingredient, the following REIC/Dkk-3 DNA:

(c) DNA consisting of the nucleotide sequence represented by SEQ ID NO: 1; or

(d) DNA that hybridizes under stringent conditions to DNA consisting of a nucleotide sequence complementary to the nucleotide sequence represented by SEQ ID NO: 1 and encodes a protein having apoptosis activity.

-   [4] A therapeutic agent for prostate cancer, comprising the     apoptosis-inducing agent according to [3]. -   [5] An agent for inhibiting prostate cancer metastasis, comprising     the apoptosis-inducing agent according to [1]. -   [6] An agent for inhibiting prostate cancer metastasis, comprising     the apoptosis-inducing agent according to [3]. -   [7] The therapeutic agent for prostate cancer according to [2] or     [4], which is used in combination with hyperthermia. -   [8] The agent for inhibiting prostate cancer metastasis according to     [5] or [6], which is used in combination with hyperthermia.

This description includes part or all of the contents as disclosed in the descriptions of Japanese Patent Application Nos. 2005-73807 and 2005-084495, which are priority documents of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an image of REIC/Dkk-3 expression in normal cells and cancer cells. The image shows REIC protein levels in normal human cells (OUMS-24: normal human fibroblast; PrSC: prostate stromal cell; and PrEC: prostate epithelial cell) and human cancer cell lines (PC3, DU145, and LNCaP: prostate cancer; KpK-1: gastric cancer cell; HeLa: cervical cancer cell; SaOS-2: osteosarcoma; and A-549: squamous carcinoma) obtained by the Western blot method. Tubulin shown in the image was used as a control.

FIG. 1B shows images of REIC/Dkk-3 expression in normal cells and cancer cells. The images show immunostaining results for the REIC/Dkk-3 protein (green) in OUMS-24 and prostate cancer cells (PC3, DU145, and LNCaP). The nuclei were stained with propiodium iodide (red).

FIG. 1C shows REIC/Dkk-3 expression in normal cells and cancer cells. In the figure, REIC/Dkk-3 mRNA levels of normal human fibroblasts and prostate cancer cell lines, which were analyzed by real-time quantitative RT-PCR, are expressed as molar ratios to those of GAPDH (p<0.05).

FIG. 1D shows images of the REIC/Dkk-3 expression in normal cells and cancer cells. The images show immunostaining results for REIC/Dkk-3 in a normal prostate, a benign hypertrophic prostate, and prostate cancer tissue sections with Gleason scores of 4 and 9.

FIG. 1E shows REIC/Dkk-3 expression in normal cells and cancer cells. The figure shows quantitative analysis results for the REIC/Dkk-3 protein using a LandMark tissue Microarray. The abbreviation “BPH” denotes benign hypertrophic prostate tissue and the abbreviation “G” denotes a Gleason score (*p<0.05; **p<0.01).

FIG. 1F shows REIC/Dkk-3 expression in normal cells and cancer cells. The figure shows quantitative analysis results for the REIC protein in fresh human prostate cancer tissue sections with Gleason scores of 7 or higher and 7 or lower. The abbreviation “BPH” denotes benign hypertrophic prostate tissue and the abbreviation “G” denotes a Gleason score (*p<0.05; **p<0.01).

FIG. 2A shows an image of apoptosis induction in human prostate cancer cells caused by REIC/Dkk-3 overexpression. The image shows REIC/Dkk-3 protein expression in prostate cancer cells (PC3) 36 hours after REIC/Dkk-3 cDNA transfection using an adenovirus vector. OUMS-24 was used as a positive control. The abbreviation “Ad-lacZ” denotes an adenovirus vector carrying lacZ.

FIG. 2B shows images of apoptosis induction in human prostate cancer cells caused by REIC/Dkk-3 overexpression. The images show TUNEL staining (green) results for normal human prostate cell lines (OUMS-24, PrEC, and PrSC) and prostate cancer cell lines (PC3, DU145, and LNCaP) 36 hours after transfection at 10 MOI. The right upper image shows results of Hoechst 33258 staining (blue).

FIG. 2C shows apoptosis induction in human prostate cancer cells caused by REIC/Dkk-3 overexpression. The figure shows percentages of TUNEL-staining-positive cells in normal human prostate cell lines (OUMS-24, PrEC, and PrSC) and those in prostate cancer cell lines (PC3, DU145, and LNCaP) 36 hours after transfection at 10 MOI.

FIG. 2D shows an image of apoptosis induction in human prostate cancer cells caused by REIC/Dkk-3 overexpression. The image shows DNA fragments observed in PC3 cells transfected with Ad-REIC at 1 MOI or higher.

FIG. 3A shows images of the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The images show TUNEL-staining results for PC3 cells 36 hours after transfection with REIC or lacZ at 10 MOI. A peptide inhibitor (V5) for Bax was added at 200 μM to a medium 1 hour prior to transfection. The scale bar corresponds to 200 μm.

FIG. 3B shows the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The figure shows effects of apoptosis inhibition in PC3 cells caused by a Bax inhibitor V5. The number of TUNEL-positive cells was determined under the same conditions used in 3A.

FIG. 3C shows images of the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The images shows immunostaining results for the Bax protein in PC3 cells 36 hours after administration of a vector at 10 MOI. Intracellular localization of mitochondria was visualized by staining using a Mitotracker (Mt).

FIG. 3D shows images of the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The images show TUNEL-staining results for PC3 cells treated in the same manner as was used for the examination of FIG. 3A. A JNK inhibitor SP600125 was used at 10 nM.

FIG. 3E shows the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The figure shows effects of inhibition of REIC/Dkk-3-induced apoptosis by the JNK inhibitor SP600125. The number of TUNEL-positive cells was determined under the same conditions used in 3C.

FIG. 3F shows an image of the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The image shows results of Western blot analysis of proteins in PC3 cells as described in 3D. The abbreviation “P” denotes “phosphorylated,” the abbreviation “Cyto c” denotes cytochrome c, and the abbreviation “β-cat” denotes β-catenin.

FIG. 3G shows an image of the involvement of Bax and JNK in apoptosis induction in PC3 cells caused by Ad-REIC. The image shows results of Western blot analysis of proteins in cytoplasm and mitochondria extracted from PC3 cells as described in FIG. 3D.

FIG. 4A shows images of effects of Ad-REIC on the growth of PC3 cells in nude mice. The images show appearances of tumors at the end of the observation period.

FIG. 4B shows effects of Ad-REIC on the growth of PC3 cells in nude mice. The figure shows the mean volume of tumors of 5 nude mice. The insert figure in FIG. 4B shows tumor volumes for mice subjected to REIC injection. 30 days after virus injection, tumors disappeared in 4 out of 5 mice.

FIG. 4C shows images of effects of Ad-REIC on the growth of PC3 cells in nude mice. The images show TUNEL-staining results for tumor tissue sections 30 days after virus injection. P1 was stained with propiodium iodide for visualization of nuclei.

FIG. 5 shows images of localized tumor-inhibitory activity of the REIC gene in orthotopic transplantation models of prostate cancer.

FIG. 6 shows localized tumor-inhibitory activity of the REIC gene in orthotopic transplantation models of prostate cancer.

FIG. 7A shows images of apoptosis-inducing effects of the REIC/Dkk-3 gene.

FIG. 7B shows apoptosis-inducing effects of the REIC/Dkk-3 gene.

FIG. 8 shows effects of prostate cancer metastasis inhibition by the REIC/Dkk-3 gene as expressed in metastasis rates.

FIG. 9 shows effects of prostate cancer metastasis inhibition by the REIC/Dkk-3 gene as expressed in total numbers of metastatic sites.

FIG. 10 shows a zymographic image of effects of matrix metalloproteinase activity inhibition by the REIC/Dkk-3 gene.

FIG. 11 shows effects of the REIC/Dkk-3 gene upon survival rates of mice inoculated with prostate cancer cells.

FIG. 12 shows images of apoptosis induction in normal cells caused by the combined use of the REIC/Dkk-3 gene and an HSP inhibitor or an HSP inducer.

FIG. 13 shows images of apoptosis induction in prostate cancer cells caused by the combined use of the REIC/Dkk-3 gene and an HSP inhibitor or an HSP inducer.

FIG. 14 shows images of effects of the combined use of the REIC/Dkk-3 gene and hyperthermic treatment in prostate cancer cells.

BEST MODE FOR CARRYING OUT THE INVENTION

The apoptosis-inducing agent of the present invention comprises, as an active ingredient, the REIC/Dkk-3 gene or a protein encoded by the gene (REIC/Dkk-3 protein).

The nucleotide sequence of the REIC/Dkk-3 gene and the amino acid sequence of the protein encoded by the gene are represented by SEQ ID NO: 1 and SEQ ID NO: 2, respectively.

As a protein encoded by the REIC/Dkk-3 gene and contained in the apoptosis-inducing agent of the present invention, a protein that has an amino acid sequence that is substantially identical to the amino acid sequence represented by SEQ ID NO: 2 and apoptosis inducing-activity in cancer cells can be used. Herein, examples of such substantially identical amino acid sequence include: an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO: 2 by substitution, deletion and/or addition of 1, several, or more (1 to 10, preferably 1 to 5, and further preferably 1 or 2) amino acids; and an amino acid sequence having a homology of at least 85% or more, preferably 90% or more, further preferably 95% or more, and particularly preferably 97% or more to the aforementioned amino acid sequence upon calculation by BLAST (Basic Local Alignment Search Tool at the National Center for Biological Information, U.S.A.) or the like (with the use of a default (default setting) parameter, for example).

In addition, examples of REIC/Dkk-3 DNA contained in the apoptosis-inducing agent of the present invention include: DNA that hybridizes under stringent conditions to DNA having a nucleotide sequence complementary to the nucleotide sequence represented by SEQ ID NO: 2; DNA having a homology of at least 85% or more, preferably 90% or more, further preferably 95% or more, and particularly preferably 97% or more to the nucleotide sequence represented by SEQ ID NO: 2 upon calculation by BLAST (Basic Local Alignment Search Tool at the National Center for Biological Information, U.S.A.) or the like (with the use of a default (default setting) parameter, for example); and DNA encoding a protein comprising an amino acid sequence derived from the amino acid sequence of a protein encoded by the aforementioned DNA by substitution, deletion and/or addition of 1, several, or more (1 to 10, preferably 1 to 5, and further preferably 1 or 2) amino acids. As long as such DNA encodes a protein having activity of inducing cancer cell apoptosis, it can be contained in the apoptosis-inducing agent of the present invention. The term “stringent conditions” used herein refers to, for example, stringent conditions (1XSSC, 0.1% SDS, 37° C.) or conditions comparable thereto, more stringent conditions (0.5XSSC, 0.1% SDS, 42° C.) or conditions comparable thereto, or even more stringent conditions (0.2XSSC, 0.1% SDS, 65° C.) or conditions comparable thereto. As such hybridization conditions become more stringent, it can be expected that DNA having a high homology to a probe sequence is more likely to be isolated. Note that the above combinations of SSC, SDS, and temperature are mere examples. Thus, a necessary level of stringency can be achieved with the use of an adequate combination of probe concentration, probe length, hybridization reaction time, and the like.

Further, an REIC/Dkk-3 protein and REIC/Dkk-3 DNA, which are contained in the apoptosis-inducing agent, the therapeutic agent for prostate cancer, and the agent for inhibiting prostate cancer metastasis of the present invention, include: a peptide having apoptosis-inducing activity, which is a fragment peptide comprising a partial amino acid sequence of the amino acid sequence of the protein; and a nucleotide encoding a peptide having apoptosis-inducing activity, which is a fragment nucleotide comprising a partial nucleotide sequence of the nucleotide sequence of the DNA, respectively. Such fragment peptide or fragment nucleotide can be readily obtained by cleaving a full-length protein or full-length DNA at an adequate position and detecting the presence or absence of apoptosis-inducing activity in the resulting fragment.

The REIC/Dkk-3 protein of the present invention is administered to a test subject and then incorporated into prostate cancer cells so that the protein acts in the cancer cells and induces apoptosis. The REIC/Dkk-3 protein can be incorporated into prostate cancer cells in a manner such that the REIC/Dkk-3 protein is allowed to bind to, for example, a cell-membrane-permeable peptide such that the protein is administered to a prostate cancer tissue site. A variety of cell-membrane-permeable peptides that have been known to the public can be used. Examples of such peptides include an HIV-1-TAT cell-membrane-permeable domain (protein transduction domain), a cell-membrane-permeable domain of the Drosophila homeobox protein antennapedia, a C-terminal (267-300) peptide of VP22, an HIV-1/Rev (34-50) peptide, an FHV/coat (35-49) peptide, and an N-terminal (7-22) hydrophobic domain of K-FGF. In addition, it is also possible to allow the REIC/Dkk-3 protein to bind to a compound that can specifically bind to cancer cells for administration. In such case, such protein-bound compound may be topically administered to a prostate cancer tissue site or may be administered orally or via other routes, such that the REIC/Dkk-3 protein can be delivered to prostate cancer cells. Examples of such compound that can specifically bind to cancer cells include a homing signal peptide, which is a peptide that binds to a receptor expressed on the cancer cell surface. Examples of such homing signal peptide include NGR and RGD, which specifically bind to a homing signal peptide receptor of an angiogenetic endothelial cell (Nat Med. 1999 Sep; 5(9): 1032-1038). For instance, in order to allow the above cell-membrane-permeable peptide or homing signal peptide to bind to the REIC/Dkk-3 protein, DNA encoding the REIC/Dkk-3 protein and DNA encoding the above cell-membrane-permeable peptide or homing signal peptide are ligated to each other in-frame such that a fusion protein can be produced by conventional genetic engineering techniques.

The REIC/Dkk-3 gene can be obtained from human cells, human tissue, or the like based on sequence information of SEQ ID NO: 1. In addition, it can be obtained according to WO01/038523.

Further, the present invention encompasses a vector comprising REIC/Dkk-3 DNA. When a test subject is transfected with such vector, the REIC/Dkk-3 protein is expressed in the test subject such that apoptosis-inducing effects can be exerted. Such transfection of a gene of interest into a test subject upon gene therapy can be carried out in accordance with conventional methods. Examples of a method for gene transfection into a test subject include a method using a viral vector and a method using a nonviral vector. A variety of such methods have been known to the public (Experimental Medicine (additional volume), Basic Techniques for Gene Therapy (Idenshi Chiryo no Kiso Gijutsu), Yodosha Co., Ltd., 1996; Experimental Medicine (additional volume), Experimental Methods for Gene Transfection & Expression Analysis (Idenshi Donyu & Hatsugen Kaiseki Jikkenho), Yodosha Co., Ltd., 1997; “Handbook for Gene Therapy Research and Development” (Idenshi Chiryo Kaihatsu Kenkyu Handbook), edited by the Japan Society of Gene Therapy, NTS Inc., 1999).

In typical methods, viral vectors used for gene transfection such as adenovirus, adeno-associated virus, and retrovirus are used. Gene transfection into cells can be carried out by introducing a gene of interest into a DNA or RNA virus such as detoxicated retrovirus, herpesvirus, vaccinia virus, poxvirus, poliovirus, Sindbis virus, Sendai virus, SV40, or human immunodeficiency virus (HIV) and allowing the obtained recombinant virus to infect cells.

When the gene of the present invention is used for a gene therapy using a virus, an adenovirus vector is preferably used. For instance, adenovirus vectors are characterized in that:

(1) gene transfection can be carried out in a variety of cells;

(2) gene transfection can be efficiently performed even in cells in growth arrest;

(3) they can be concentrated by centrifugation such that a virus at high titer (10 to 11 PFU/ml or more) can be obtained; and

(4) they are appropriate for use for direct gene transfection into in vivo tissue cells. As an adenovirus vector used for gene therapy, the following vectors have been developed: a second generation adenovirus vector (Lieber, A., et al., J. Virol., 70, 8944, 1996; Mizuguchi, H. & Kay, M. A., Hum. Gene Ther., 10, 2013, 1999) obtained by deleting the E2 or E4 domain in addition to the E1/E3 domain from a first generation adenovirus vector lacking the E1/E3 domain (Miyake, S., et al., Proc. Natl. Acad. Sci. U.S.A., 93, 1320, 1996); and a third generation adenovirus vector (Steinwaerder, D. S. et al., J. Virol., 73, 9303, 1999) almost completely lacking the adenovirus genome (GUTLESS). However, for transfection of the gene of the present invention, any adenovirus vector may be used without particular limitation. Further, the gene of the present invention can be applied for long-term gene expression using, for example, an adeno-AAV hybrid vector having the ability to cause incorporation in the AAV chromosome (Recchia, A. et al., Proc. Natl. Acad. Sci. U.S.A., 96, 2615, 1999) and an adenovirus vector that has acquired the ability to cause incorporation in the chromosome with the use of a transposon gene. In addition, by inserting a peptide sequence that can be translocated to an H1 loop of an adenovirus fiber in a tissue-specific manner, it is possible to impart tissue specificity to an adenovirus vector (Mizuguchi, H. & Hayakawa, T., Nippon Rinsho, 7, 1544, 2000).

Further, even without the use of the above viruses, it is possible to transfect cells or tissue with a gene of interest with the use of a recombinant expression vector comprising a gene expression vector, such as a plasmid vector. For instance, gene transfection into cells can be performed by a lipofection method, a calcium phosphate coprecipitation method, a DEAE-dextran method, and a DNA direct injection method using a micro glass tube. Furthermore, it is possible to allow a recombinant expression vector to be incorporated into cells by a gene transfection method using internal liposomes, a gene transfection method using electorostatic type liposomes, an HVJ-liposome method, a modified HVJ-liposome method (HVJ-AVE liposome method), a method using an HVJ-E (envelope) vector, a method of introducing a receptor-mediated gene, a method of transferring DNA molecules into cells with carriers (metallic particles) using a particle gun, a method of direct transfection of naked DNA, a transfection method using a variety of polymers, or the like. The expression vector used in such case may be any expression vector as long as it can cause in vivo expression of a gene of interest. Examples thereof include expression vectors such as pCAGGS (Gene 108, 193-200 (1991)), pBK-CMV, pcDNA3.1, pZeoSV (Invitrogen Corporation, Stratagene), and pVAX1.

A vector comprising REIC/Dkk-3 DNA may adequately comprise a promoter or enhancer for gene transcription, a polyA signal, a marker gene used for labeling and/or selection of cells transfected with a gene, or the like. In such case, examples of a promoter that can be used include conventional promoters.

In order to introduce a pharmaceutical composition comprising REIC/Dkk-3 DNA of the present invention into a test subject, the following methods or the like may be used: an in vivo method, wherein a gene therapeutic agent is directly introduced into a living body; and an ex vivo method, wherein a specific cell is collected from a human, a gene therapeutic agent is introduced ex vivo into the cell, and the cell is introduced into the human (Nikkei Science, 1994, 4, pp. 20-45; The Pharmaceuticals Monthly, 36(1), 23-48 (1994); Experimental Medicine (additional volume), 12(15), (1994); “Handbook for Gene Therapy Research and Development” (Idenshi Chiryo Kaihatsu Kenkyu Handbook), edited by the Japan Society of Gene Therapy, NTS Inc., 1999).

Prostate cancer is a therapeutic target of the present invention. In particular, the present invention is especially useful for highly malignant prostate cancer. The term “highly malignant prostate cancer” used herein indicates, for example, prostate cancer with a Gleason score of 8 or higher.

The REIC/Dkk-3 protein or REIC/Dkk-3 DNA of the present invention can be further used for inhibition of prostate cancer metastasis. That is, the present invention encompasses an agent for inhibiting prostate cancer metastasis comprising, as an active ingredient, the REIC/Dkk-3 protein or REIC/Dkk-3 DNA. The agent for inhibiting prostate cancer metastasis can be used in the same manner as an apoptosis-inducing agent for prostate cancer and a therapeutic agent for prostate cancer. When administering such agent to prostate cancer cells, it is possible to inhibit prostate cancer metastasis.

Further, the REIC/Dkk-3 protein or REIC/Dkk-3 DNA can enhance effects of hyperthermia for prostate cancer. Hyperthermia is a cancer therapy utilizing the cancer cell characteristic of being more heat-sensitive than normal cells. Apoptosis induction by the REIC/Dkk-3 protein is associated with the expression of heat shock protein (HSP) in cells and is affected by cell stress responsiveness. That is, with the combined use of hyperthermia and an apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis that comprises, as an active ingredient, an REIC/Dkk-3 protein or REIC/Dkk-3 DNA, apoptosis is more likely to be induced so that it becomes possible to treat cancer and to inhibit cancer metastasis more effectively. Specifically, upon hyperthermic treatment of cancer regions, the apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis, which comprises, as an active ingredient, the REIC/Dkk-3 protein or REIC/Dkk-3 DNA of the present invention can be administered to the relevant regions. Any heating method may be used for a hyperthermic treatment for hyperthermia as long as it allows a prostate cancer region of a test subject to be subjected to hyperthermic treatment. Either a localized heating method or a whole-body heating method can be adopted. A heating apparatus to be used may be based on any heating method such as an external heating method, an intracavitary heating method, or a tissue heating method. A specific example of a heating apparatus is a heating apparatus equipped with a thermostatic bath and using microwaves, ultrasonic waves, electromagnetic waves, RF waves (radio-frequency waves), or the like. The temperature for hyperthermic treatment is 41° C. to 45° C. and preferably 43° C. to 44° C.

The apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis, which comprises, as an active ingredient, an REIC/Dkk-3 protein or REIC/Dkk-3 DNA of the present invention may be administered prior to, during, or after hyperthermia.

That is, the present invention encompasses a method of treating prostate cancer or inhibiting prostate cancer metastasis, comprising administering an apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis, which comprises, as an active ingredient, an REIC/Dkk-3 protein or REIC/Dkk-3 DNA to a test subject upon hyperthermic treatment of a prostate cancer region of the test subject. Further, the present invention encompasses: an apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis, which comprises, as an active ingredient, an REIC/Dkk-3 protein or REIC/Dkk-3 DNA to be used in combination with hyperthermia; and an apoptosis-inducing agent, cancer therapeutic agent, or agent for inhibiting cancer metastasis, which comprises, as an active ingredient, an REIC/Dkk-3 protein or REIC/Dkk-3 DNA, and which is administered prior to, during, or after application of hyperthermia.

The pharmaceutical composition of the present invention contains an REIC/Dkk-3 protein, a fusion protein comprising the REIC/Dkk-3 protein and a cell-membrane-permeable peptide or a homing signal peptide, REIC/Dkk-3 DNA, or a vector comprising the DNA, together with a pharmaceutically acceptable carrier, diluent, and/or excipient.

The pharmaceutical composition of the present invention can be administered in various forms. For instance, it can be formed into tablets, capsules, granules, powder, syrups, or the like for oral administration. Alternatively, it can be formed into injections, infusions, suppositories, sprays, eye drops, nasal preparations, adhesive preparations, or the like for parenteral administration.

The pharmaceutical composition of the present invention may be topically administered. For instance, the effects thereof can be exerted when the composition is administered to cancer regions by, for example, injection.

The pharmaceutical composition of the present invention contains a carrier, a diluent, and/or an excipient, which are usually used in the pharmaceutical field. Examples of a carrier and an excipient used for tablets include lactose and magnesium stearate. Examples of aqueous liquid used for injection include physiological saline and isotonic solutions containing glucose or different adjuvants, which may be used in combination with adequate solubilizers, including alcohol, polyalcohol such as propylene glycol, and nonionic surfactants. Examples of oily liquid that can be used include sesame oil and soybean oil. Examples of a solubilizer that may be used in combination include benzyl benzoate and benzyl alcohol.

The dose of the pharmaceutical composition of the present invention is determined depending upon patient's symptoms, age, and weight, and the like. Upon oral administration, the daily dose in terms of an REIC/Dkk-3 protein is approximately 0.001 mg to 100 mg. It may be administered in a single dose or multiple doses. In addition, upon parenteral administration, it is possible to carry out subcutaneous, intramuscular, or intravenous administration at 0.001 mg to 100 mg in a single dose. In addition, REIC/Dkk-3 DNA that is inserted into an expression vector or the like so as to be translated in a test subject may be subcutaneously, intramuscularly, or intravenously administered at 0.001 mg to 100 mg in a single dose every several days, weeks, or months.

EXAMPLES

The present invention is hereafter described in greater detail with reference to the following examples, although the technical scope of the present invention is not limited thereto.

Example 1

Prostate Cancer Cell Apoptosis Induction by REIC/Dkk-3

Materials used in the Examples of the present invention were obtained as described below. The Examples were carried out by methods described below.

Cells and Culture Method

Normal prostate epithelial cells (PrEC) and prostate stromal cells (PrSC) were purchased from Cambrex (Baltimore, Md.). The prostate cancer cell lines PC3, DU145, and LNCaP were provided by ATCC (Rockville, Md.). OUMS-24 was provided by Dr. Masayoshi Nanba. An HAM'S F-12 K medium, an RPMI 1640 medium, and modified MEM medium (Nissui) were separately used with a supplement of 10% calf serum for PC3, DU145 and LNCaP, and OUMS-24.

Human Prostate Tissue

A LandMark™ low-density prostate tissue microarray (Ambion, Austin) was used for immunostaining of the REIC/Dkk-3 gene. Fresh prostate cancer tissue samples were obtained from 40 patients. Of them, 20 samples had a Gleason score of 8 or higher and another 20 samples had a Gleason score of 7 or lower. Immunological analyses

After fixation with 4% paraformaldehyde, the cells and the tissue samples were immunostained with a primary antibody (anti-human REIC/Dkk-3 antibody purified in the laboratory of the present inventors) and a secondary antibody (FITC-conjugated anti-rabbit immunoglobulin G antibody, Sigma, St. Louis). For Bax and Bcl-2, an anti-human Bax antibody (Upstate Cell signaling solutions, Lake Placid, N.Y.) and an anti-human Bcl-2 antibody (BD Biosciences, San Diego) were used, respectively. A Vectashield mounting medium with DAPI or with propiodium iodide (Vector Laboratories, Burlingame, Calif.) was used for staining of cell nuclei. The signal intensity of each stained sample was quantitated using computer software. Western blot analysis was performed as previously described. The antibodies used were as follows: a purified rabbit anti-human REIC/Dkk-3 antibody; an Apoptosis sampler I kit (BD Biosciences) for Apf-1, Bad, Bcl-2, Bcl-xL, and p 53; a rabbit anti-human Bax antibody (Upstate Cell signaling solutions, Lake Placid, N.Y.); a rabbit anti-human Bax antibody (BD Biosciences); a mouse anti-human Apaf-1 antibody (BD Biosciences); and a mouse anti-human tubulin antibody (Sigma).

Real-Time Quantitative RT-PCR

Real-time PCR was performed under the conditions recommended by the manufacturer using a LightCycler™ (Roche Diagnostic, Lewes, UK). The primers used for real-time PCR were as follows:

REIC/Dkk-3-F′ 5′-GTAAGTTCCCCTCTGGCTTG-3′; (SEQ ID NO: 3) REIC/Dkk-3-R′ 5′-AAGCACCAGACTGTGAAGCCT-3′; (SEQ ID NO: 4) GAPDH-F′ 5′-GGGTGTGAACCATGAGAAGTATGA-3′; (SEQ ID NO: 5) and GAPDH-R′ 5′-TGCTAAGCAGTTGGTGGTGC-3′. (SEQ ID NO: 6)

The obtained products were checked by melting point analysis, electrophoresis, and direct sequencing. Standard curves were created using the plasmids containing the respective inserts. The results are shown as molar ratios of REIC/Dkk-3 to GAPDH.

Apoptosis Analyses

A DNA ladder method was performed under conventional conditions. DNA was extracted after lysing cells with Triton X-100, treated with RNase and proteinase K, and electrophoresed on 2% agarose gel. An In Situ Cell Death Detection Kit, Fluorescein (Roche) was used for TUNEL staining. A Bax-specific peptide inhibitor V5 was purchased from Sigma Genosis (Woodlands, Tex.).

Animal Experiments

PC3 cells (2.5×10⁶/PBS 50 μl) were subcutaneously injected into the right flanks of 8-week-old BALB/C nude mice. One week later, when the tumor diameters had reached 5 mm, adenovirus vectors (2.5×10⁸ pfu) incorporating the REIC gene (or LacZ gene) were injected intratumorally. The same volume of PBS was injected for controls. Tumor sizes were measured every 3 days up to 30 days after adenovirus vector injection. Tumor volumes (V) were calculated using the following formula: ½×(the shorter diameter)²×(the longer diameter).

In this Example, results described below were obtained.

In order to find the potential usefulness of the REIC/Dkk-3 gene as a therapeutic target, a variety of cells were first examined in terms of REIC/Dkk-3 gene expression. In human fibroblasts (OUMS-24), prostate epithelial cells (PrEC), and prostate stromal cells (PrSC), the REIC/Dkk-3 protein was detected in two bands of 62 to 83 kDa (FIG. 1A). The observed size was larger than the size estimated from the amino acid sequence (38.3 kDa) because of glycosylation. The REIC/Dkk-3 protein was barely detected in cancer cell lines, excluding 3 representative prostate cancer cell lines (PC3, LNCaP, and DU145) and 4 prostate cancer cell lines. Lack of REIC/Dkk-3 protein in the 3 different prostate cancer cell lines was confirmed by immunostaining (FIG. 1B). Downregulation of REIC/Dkk-3 mRNA was also confirmed by Quantitative RT-PCR (FIG. 1C).

The expression of the REIC/Dkk-3 gene was examined in human prostate tissue by immunostaining (FIG. 1D). The REIC/Dkk-3 protein was detected in epithelial cells and stromal cells in normal prostates and benign hypertrophic prostates. In prostate cancer with a Gleason score of 7 or lower, the REIC/Dkk-3 protein level was reduced differently. In prostate cancer with a Gleason score of 8 to 10, the expression of REIC/Dkk-3 protein was not observed. Signal intensity was quantitatively measured using computer software (FIG. 1E). In both a commercially available prostate tissue microarray (FIG. 1E, left) and fresh prostate cancer tissue (FIG. 1E, right), the expression level of REIC/Dkk-3 protein was reduced in proportion to the cancer grade. Upon immunostaining of other normal human tissues (from the brain, heart, liver, pancreas, kidney, mammary glands, and lymph nodes), the REIC/Dkk-3 protein was expressed at different intensities.

In order to examine the possible use of the REIC/Dkk-3 gene as a gene therapy tool, the REIC/Dkk-3 gene was overexpressed using an adenovirus vector incorporating the REIC/Dkk-3 gene. The REIC/Dkk-3 protein level in PC3 cells transfected with REIC/Dkk-3 with the use of vectors at 1 MOI was almost comparable to that of OUMS-24 (FIG. 2A). Within a few days after transfection, most of the prostate cancer cells had become detached from the bottom of the culture vessel. In order to examine the cause, cells were stained 36 hours after REIC/Dkk-3 gene transfection by the TUNEL method. As shown in FIG. 2B, many prostate cancer cells (PC3, DU145, and LNCaP). were TUNEL-positive while fewer normal cells (OUMS-24, prostate stromal cells, and prostate epithelial cells) were TUNEL-positive. The incidences of TUNEL-positive cells were 49%, 24%, and 41% in the cases of PC3, DU145, and LNCaP, respectively. However, the incidence of TUNEL-positive cells was less than 1% in the case of normal cells (FIG. 2C). DNAs of PC3 cells were analyzed 36 hours after vector transfection so as to confirm apoptotic properties.

In the case of PC3 cells transfected with the REIC gene at 1 MOI or higher, different patterns of DNA bands were clearly observed (FIG. 2D). As shown in FIG. 2D, specific DNA fragments were observed in PC3 cells transfected with Ad-REIC at 1 MOI or higher. One day after seeding of 5×10⁵ PC3 cells, viral vectors were allowed to transfect the cells. The cells were harvested 36 hours after transfection. The transfection efficiency of Ad-REIC and the expression level of the REIC/Dkk-3 gene were similar among the cells (data not shown). These results indicate that overexpression of REIC/Dkk-3 selectively induces apoptosis in prostate cancer cells that substantially lack endogenous REIC/Dkk-3 expression.

In order to discover the mechanism for tumor-specific apoptosis caused by the REIC/Dkk-3 gene, expression levels of different apoptosis/cell-cycle-regulation-related proteins in PC3 cells and OUMS-24 cells were compared. In PC3 cells transfected with the RE1C/Dkk-3 gene, reduced levels of apoptosis-inhibiting Bcl-2 and Bcl-XL proteins were observed (FIG. 3F). No significant changes in levels of Bax, Bad, ApaF-1, p 53, p 21 (CIP1/WAF1), or p 16 (INK4a) were observed among cells (data not shown).

A caspase 8 inhibitor did not inhibit Ad-REIC-induced apoptosis in PC3 cells. Meanwhile, a Bax inhibitor V5 (Sawada, M. et al., Nat Cell Biol 5, 352-7 (2003)) completely inhibited apoptosis (FIG. 3A). Translocation of Bax protein from cytoplasm to mitochondria may trigger activation of a Bax-mediated apoptotic pathway (Gross, A. et al., Embo J 17, 3878-85 (1998)). FIG. 3C shows mitochondrial translocation of Bax protein by Ad-REIC and inhibition of such translocation by V5. V5 showed no effects on the protein levels of Bcl-2 and Bax.

It has been known that c-jun N-terminal kinase (JNK) mediates a non-canonical pathway of Wnt signaling (Lei, K. et al., Mol Cell Biol 22, 4929-42 (2002); and Tsuruta, F. et al., Embo J 23, 1889-99 (2004)). Further, it has been reported that Bax plays an important role in JNK-induced apoptosis and JNK promotes mitochondrial translocation of Bax. When a JNK-specific inhibitor SP600125 was added to PC3 cells, Ad-REIC-induced apoptosis was inhibited in a concentration-dependent manner (FIGS. 3D and 3E). Activation of JNK in PC3 cells infected with Ad-REIC was confirmed using a phosphorylated JNK antibody (FIG. 3F). SP600125 inhibited JNK kinase activity but not phosphorylation of JNK itself. Bax was detected in cytoplasm of PC3 cells but clearly observed to be translocated to mitochondria in Ad-REIC-infected cells (FIG. 3G). The mitochondrial translocation of Bax was associated with the release of cytochrome c into cytoplasm and was suppressed by a JNK inhibitor SP600125. Phosphorylated JNK was also translocated by Ad-REIC to mitochondria. These results suggest that overexpression of REIC activates JNK, reduces the Bcl-2 protein level, promotes mitochondrial translocation of Bax protein, releases cytochrome c into cytoplasm, and finally induces apoptosis. Recently, Hsieh et al. reported that overexpression of REIC/Dkk-3 gene induces apoptosis in different human cancer cells through activation of caspase 3, which is known as a major apoptosis executor downstream of cytochrome c (Hsieh, S. Y. et al., Oncogene 23, 9183-9 (2004)).

At present, it is unclear whether Ad-REIC-induced JNK activation directly or indirectly acts on Bcl-2 and Bax, although Bcl-2 (Yamamoto, K. et al., Mol Cell Biol 19, 8469-78 (1999); and Deng, X. et al., J Biol Chem 276, 23681-8 (2001)), Bcl-XL (Basu, A. et al., FEBS Lett 538, 41-7 (2003)), and Bim (Lei, K. et al., Mol Cell Biol 22, 4929-42 (2002)) have been identified as targets for JNK. It was confirmed that the REIC/Dkk-3 protein was glycosylated and secreted into a culture solution when overexpressed in PC3 cells by Ad-REIC. The amount of β-catenin and the intracellular localization thereof were not affected by Ad-REIC. Thus, it is considered that secreted REIC/Dkk-3 is unlikely to act through the Wnt canonical pathway (data not shown). JNK are thought to be activated through the non-canonical pathway of Wnt signaling or by an intracellular stress sensing system for the overexpressed protein or unknown intracellular factors. In practice, an IL-10 family cytokine (intercellular signal transduction protein) MDA-7/IL-24 (also referred to as MDA7/IL-24) efficiently induces apoptosis in many types of human cancer cells (particularly human prostate cancer cells) even when secretion of the cytokine is blocked (Sauane, M. et al., Cancer Res 64, 2988-93 (2004)). Bax is activated by p 53 (Han, J. et al., Genes Dev 10, 461-77 (1996)). However, since PC3 cells are null in p 53, apoptosis induction by the REIC gene is independent of the p 53 function (Arah, I. N. et al., Anticancer Res 18, 1845-9 (1998)). MDA-7 also selectively induces apoptosis by p53-independent activation of Bax (Su, z. z. et al., Proc Natl Acd Sci U.S.A. 95, 14400-5 (1998)). Recently, Hoang et al. reported that the overexpression of the REIC/Dkk-3 gene did not induce apoptosis in a human osteosarcoma cell line Saos-2 but inhibited invasion and motility of the cells in in vitro experiments (Hoang, B. H. et al., Cancer Res 64, 2734-9 (2004)). REIC/Dkk-3 may exert its anticancer activity at different points.

Since apoptosis induction by REIC/Dkk-3 gene transfection was proved by in vitro studies, the effect of the REIC/Dkk-3 gene upon PC3 cells was examined in vivo (in animal experiments). PC3 cells (2.5×10⁶) were subcutaneously injected into nude mice. One week later, when the tumor volumes reached 30 to 100 cm³, 2.5×10⁸ pfu of REIC or lacZ was injected intratumorally with the use of adenovectors. The same volume of buffer (PBS) was injected into a control group. Tumor sizes were measured every 3 days during the 27 days following injection. Tumors in the control group and the lacZ group grew gradually during the observation period of 1 month after injection (FIGS. 4A and 4B). In contrast, tumors completely disappeared in 4 out of 5 mice in the REIC group (treatment group). Further, tumors did not completely disappear in 1 out of 5 mice in the REIC group; instead, they shrunk and then remained unchanged over the observation period. The above tumors were resected after the end of the observation period, followed by TUNEL staining (FIG. 4C). No apoptosis was observed in the buffer group or the lacZ group. Meanwhile, in the REIC group, many TUNEL-positive cells were observed 1 month after injection. Selective apoptosis-inducing activity in culture cells and in vivo tumor-inhibitory activity that are exerted by the REIC/Dkk-3 gene strongly indicate that the REIC/Dkk-3 gene can be a target for cancer therapies in addition to p 53 and mda-7 (Sauane, M. et al., Cancer Res 64, 2988-93 (2004)). Prostate cancer is one of the most common malignant diseases in Western countries. Various therapeutic measures, including hormone therapies, have been applied to prostate cancer. However, once prostate cancers acquire hormone resistance at later stages, it is difficult to control them by conventional therapies.

This Example indicates that REIC/Dkk-3 can be a new molecular target to counteract highly malignant prostate cancers.

Example 2

Effects of Prostate Cancer Metastasis Inhibition caused by REIC/Dkk-3 Gene Transfection using Adenovirus Vectors

Mouse prostate cancer cells RM-9 (5.0×10³ cells) were injected into prostates of C57BL/6 mice. One week later, 1.2×10⁸ pfu of REIC or lacZ (or PBS) was directly injected intratumorally (mean tumor diameter: 60 mm3) with the use of adenovectors. Tumor growth was significantly inhibited in the REIC/Dkk-3 group (treatment group) compared with the control group and the lacZ group (FIGS. 5 and 6). Tumor diameters were measured every 3 days using a transrectal ultrasonography system previously developed by the present inventors. Tumor volumes (V) were calculated by the following formula: ½×(short diameter)²×(long diameter). FIG. 5 shows ultrasound images and images of mouse intraperitoneal cavities taken with the transrectal ultrasonography system. FIG. 6 shows time-dependent changes in tumor volumes. As shown in FIGS. 5 and 6, stronger tumor inhibition effects were observed in the REIC/Dkk-3 group than were observed in the LacZ group.

The above tumors were resected on days 10 and 16 (3 and 9 days after adenovector injection, respectively), followed by TUNEL staining for detection of apoptotic cells. As a result, a greater number of cells were found to be TUNEL-positive in the REIC/Dkk-3 group compared with the buffer group and the LacZ group (FIGS. 7A and 7B).

Subsequently, in order to analyze metastasis-inhibitory activity of the REIC gene, each group was subjected to laparotomy when prostate cancer volumes reached 750 mm³. Then, intrapelvic lymph nodes were observed. In order to confirm metastasis rates when volumes of primary tumor lesions reached the same level, prostate cancer volumes were measured using transrectal ultrasonography. When tumor diameters reached 750 mm³ in each group, laparotomy was carried out so that intrapelvic lymph nodes were collected. In the control group and the lacZ group, 80% to 85% of mice were found to experience lymph node metastasis. Meanwhile, in the REIC/Dkk-3 group, approximately 40% of mice were found to experience such metastasis (PBS: n=10; Lacz: n=12; and REIC/Dkk-3: n=12) (FIG. 8). Further, the number of lymph node metastasis lesions was counted. The number of lymph node metastasis lesions was 0 to 5 (mean value: 4) in the control group and the lacZ group; however, it was 0 to 2 (mean value: 1) in the REIC/Dkk-3 group (PBS: n=10; Lacz: n=12; and REIC/Dkk-3: n=12)(FIG. 9).

Subsequently, in order to examine the mechanism for metastasis-inhibitory activity of the REIC/Dkk-3 gene, RM-9 was transfected in vitro with REIC/Dkk-3 or lacZ with the use of adenovectors. Then, matrix metalloproteinase (MMP) activity in a culture solution was measured by zymography. The term “zymography” used herein refers to a representative technique for detecting activity of MMP (matrix metalloproteinase) which is a collagen-degrading enzyme that exists in a basal membrane, such activity serving as an index of the invasion/metastasis ability of cancer cells. A culture supernatant or the like is added to gel containing modified collagen (gelatin) that is a substrate for MMP, followed by migration. Then, a reaction solution that activates MMP is added thereto to stain the gel so that bands appear in connection with the presence of enzymatic activity. MMP2 (72 kDa) and MMP9 (92 kDa) are closely associated with basal membrane invasion. RM-9 was transfected with LacZ, human REIC, or the mouse REIC gene at 10 MOI with the use of adenovectors. 6 hours after transfection, the culture solution used was exchanged and the newly exchanged culture solution was collected 42 hours later, followed by zymography. As shown in FIG. 10, significant signal reduction was observed in the REIC/Dkk-3 group compared with the lacZ group. The results indicate that the matrix protease activity was reduced. Thus, it was suggested that such reduction in MMP activity is involved in the metastasis inhibition effects of the REIC/Dkk-3 gene.

Regarding survival curves for orthotopic transplantation models of prostate cancer, survival was significantly extended in the REIC/Dkk-3 group compared with the control group and the LacZ group. As a result of single-dose administration of the REIC/Dkk-3 gene, the improvement was observed in survival rates in addition to effects of localized tumor inhibition and metastasis inhibition (FIG. 11).

The longest survival time extension effect was obtained in the above case compared with the results of gene therapy experiments using the other genes (HSV-tk and IL-12) and the same system (Median survival: control group=22 to 25 days; REIC/Dkk-3 treatment group=42 to 50 days; HSV-tk treatment group=26 days (Prostate Cancer and Prostatic Diseases, 4: 44-55, 2001); and IL-12 treatment group=28 days (Gene Therapy 6: 338-349, 1999)).

Example 3

Relationship between HSP70 and Apoptosis Induction caused by Forced Expression of REIC/Dkk-3

It was examined whether tumor selectivity in terms of apoptosis expression caused by Ad-REIC would be associated with HSP70 expression in normal cells and cancer cells.

Normal cells OUMS 24 (human immortalized fibroblast) and prostate cancer cells PC3 were used for comparison. The cells were infected with Ad-REIC at 20 MOI. 24 hours later, an HSP70 inhibitor (heat shock protein inhibitor I, CALBIOCHEM, BIOCHEMICALS) and an HSP70 inducer (Geranyl-Geranyl Acetone) (250 mM each) were separately added to a culture solution. 48 hours later, TUNEL staining was performed to determine influence upon apoptosis. FIGS. 12 and 13 show staining images for OUMS24 and of PC3, respectively. In FIGS. 12 and 13, images on the left side indicate TUNEL-staining results and images on the right side indicate DAPI-staining results. As shown in FIG. 12, among normal cells OUMS24, a large number of TUNEL-positive cells were obtained with the combined use of the Ad-REIC and the HSP70 inhibitor. On the other hand, a small number of TUNEL-positive cells were obtained with the combined use of the Ad-REIC and the HSP inducer. Also, as shown in FIG. 13, among prostate cancer cells PC3, the number of TUNEL-positive cells obtained with the combined use of the Ad-REIC and the HSP70 inhibitor was greater than that obtained with the use of Ad-REIC alone. On the other hand, the number of TUNEL-positive cells obtained with the combined use of the Ad-REIC and the HSP inducer was smaller than that obtained with the use of Ad-REIC alone. That is, apoptosis was induced in normal cells with the use of the HSP70 inhibitor in combination. On the other hand, apoptosis expression was inhibited in cancer cells with the use of the HSP70 inducer in combination. Further, apoptosis induction was promoted with the use of the HSP70 inhibitor in combination.

The above results revealed that apoptosis expression caused by Ad-REIC significantly depends on cell stress responsiveness.

Example 4

PC3 cells and OUMS-24 cells were separately infected with viruses (Ad-LacZ/Ad-REIC) at 20 MOI for 36 hours. Thereafter, the cells were separately placed on media at 45° C. and then the media were placed in an incubator at 45° C. for 6 hours, followed by CBB staining. The cells subjected to heat treatment at 45° C. belong to a heat (+) group (group subjected to hyperthermia following infection). In addition, cells that had not been heat-treated (heat (−) group) were infected with viruses for 42 hours, followed by staining.

Almost all PC3 cells in the group subjected to hyperthermia following infection completely died (FIG. 14). Since cancer cells are generally sensitive to hyperthermia, synergistic effects can be obtained by a therapy involving combined use of cancer hyperthermia, which has been widely examined in medical practice, and the apoptosis- inducing agent of the present invention.

INDUSTRIAL APPLICABILITY

As shown in the Examples, the REIC/Dkk-3 expression level was specifically reduced in highly malignant prostate cancer tissue. In addition, apoptosis was selectively induced in cancer cells by transfecting the REIC/Dkk-3 gene into prostate cancer cells lacking REIC/Dkk-3 expression so as to cause REIC/Dkk-3 expression in such cells. Further, when nude mice into which human prostate cancer cells had been implanted for tumor development were transfected with the REIC/Dkk-3 gene, tumor inhibition was observed. That is, the REIC/Dkk-3 gene of the present invention and an expression product thereof can be used as an apoptosis-inducing agent for prostate cancer cells and a therapeutic agent for prostate cancer, which can cause apoptosis in prostate cancer cells, resulting in prostate cancer inhibition. Furthermore, the REIC/Dkk-3 gene of the present invention and an expression product thereof can be used as agents for inhibiting prostate cancer metastasis, which can inhibit prostate cancer metastasis. Moreover, prostate cancer can be treated more effectively with the combined use of hyperthermia and the REIC/Dkk-3 gene of the present invention and an expression product thereof.

All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety.

Free Text of Sequence Listing

SEQ ID NOS: 3 to 6 (primers) 

1. An apoptosis-inducing agent for prostate cancer, comprising, as an active ingredient, the following REIC/Dkk-3 protein: (a) a protein consisting of the amino acid sequence represented by SEQ ID NO: 2; or (b) a protein consisting of an amino acid sequence derived from the amino acid sequence represented by SEQ ID NO: 2 by substitution, deletion, or addition of 1 or more amino acids and having apoptosis activity.
 2. A therapeutic agent for prostate cancer, comprising the apoptosis-inducing agent according to claim
 1. 3. An apoptosis-inducing agent for prostate cancer, comprising, as an active ingredient, the following REIC/Dkk-3 DNA: (c) DNA consisting of the nucleotide sequence represented by SEQ ID NO: 1; or (d) DNA that hybridizes under stringent conditions to DNA consisting of a nucleotide sequence complementary to the nucleotide sequence represented by SEQ ID NO: 1 and encodes a protein having apoptosis activity.
 4. A therapeutic agent for prostate cancer, comprising the apoptosis-inducing agent according to claim
 3. 5. An agent for inhibiting prostate cancer metastasis, comprising the apoptosis-inducing agent according to claim
 1. 6. An agent for inhibiting prostate cancer metastasis, comprising the apoptosis-inducing agent according to claim
 3. 7. The therapeutic agent for prostate cancer according to claim 2, which is used in combination with hyperthermia.
 8. The agent for inhibiting prostate cancer metastasis according to claim 5, which is used in combination with hyperthermia.
 9. The therapeutic agent for prostate cancer according to claim 4, which is used in combination with hyperthermia.
 10. The agent for inhibiting prostate cancer metastasis according to claim 6 which is used in combination with hyperthermia. 